¶ … Nuclear Fuel Cycle is a set of different processes that utilize nuclear materials and then returns them to their initial state, in a cyclical manner. It begins with the mining of naturally occurring nuclear materials from the environment, and ends with safe and proper disposal of nuclear waste products back to the environment. Production of energy from Uranium requires several unique processes. One of the terms used in this production of nuclear energy is front end, referring to the entire set of processes involved in making nuclear energy from the uranium ore in the nuclear fuel cycle. The processes involved are: [1] mining, [2] crushing, [3] processing, [4] enrichment, and [5] the fabrication of fuel. After being used to produce energy, the nuclear material is now known as spent fuel. The spent fuel has to be converted in a reprocessing or storage facility if the company wants to recycle it. Short- or long- term storage of the spent fuel, or the reprocessing of the same, are all known as the back end processes of the nuclear fuel cycle (IAEA, 2012). Uranium Ore Sources

The cycle starts with mining or extraction of uranium (U) mineral. This mineral ore contains uranium as various complex oxides. These complex oxides are then reduced to the U30s oxide. This oxide is then taken through a conversion process to form uranium hexafluoride, UF6. This is the form of uranium that is required and can undergo enrichment at isotope separation plants (Lamarsh and Baratta, 2001). Uranium deposits are found in different geological forms. The most important geological forms of Uranium are: the Proterozoic deposits which are mainly found in Australia and Canada; the roll fronts types in Mesozoic-Cenozoic deposits of the U.S.A. And Kazakhstan; and the Iron Oxide-Copper-Gold (IOCG) deposits whereby the uranium mineral is extracted as a by-product of the extraction of copper in Australia.

The mineralization process of Uranium that causes it to appear in different forms is determined by two of its properties: its high solubility in its hexavalent (U+6) state and its low solubility in a tetravalent U+4) state. The geochemical composition of Uranium is reflected in its widespread leaching by oxidized meteoric/formation waters and its precipitation in oxidized form, UO2, in redox reactions. The loss of water from the soil through evaporation and plant transpiration in arid lands can result in the enrichment of Uranium near the surface in a calcrete form of deposits, such as in Australia and Namibia. Proterozoic Quartz-pebble conglomerates are also known to contain low-grade uraninite, such as in the Canadian and South African deposits. The present confirmed uranium deposits globally are enough to sustain present and predicted nuclear energy production demand for the next one hundred years. Better and more advanced technologies in nuclear power production, such as fast neutron reactors, are expected to extend nuclear fuel lifetime to more than a thousand years (Lehmann, 2008).

Mining Environmental Considerations

The most important effect of any mining activity is its impact on the quality and flow of water in the area surrounding the mining project. The main considerations are: [1] whether both the surface and groundwater resources will remain suitable for human consumption; and [2] whether the flow of surface waters will still be sufficient to support the indigenous aquatic and terrestrial life after the mining activity. Emissions into the atmosphere are part of every process of the mining cycle such as exploration, extraction, processing, construction, and other activities. Mining activities involve large amounts of raw materials and lots of waste materials which contain minute particles that can easily be blown by wind causing health hazards (ELAW, 2015).

Mining OSHA considerations

Employees working in uranium mines are protected by regulations which place limits on their dust, noise, chemical and radiation dose exposures under the Mine Safety and Health Administration (MSHA), and the overall Occupational Safety and Health Administration (OSHA). Protection of uranium mine workers is specifically regulated by the Nuclear Regulatory Commission and is also subject to State legislation. States have full jurisdiction over mining activities on land that is not federally owned meaning that these activities are not regulated by federal agencies or policies. Additionally, different mining companies also have different policies and procedures of limiting the exposure of their workers to different hazards. Eventually the legislations or policies that regulate the mining and processing of uranium are determined by both the type and location of mining activity. Thus, a mining facility depending on its own unique features can be governed by a combination of both federal and state and/or local employee protection and environmental regulations (Carlsen et al., 2013).

Out of any amount of naturally occurring uranium, just a small percentage, 0.7%, can undergo fission, the process of producing power in a nuclear reactor. The only isotope of uranium capable of undergoing fission is the Uranium-235 (U-235). The other common isotope is the uranium-238 (U-238). Many types of reactors require an increase in concentration of U-235, often by about 3.5-5%. This process is known as isotope separation, whereby an isotope is concentrated (enriched) relative to other isotopes. For enrichment to occur, the uranium needs to be in the gaseous form. This necessitates the conversion of the uranium oxide into uranium hexafluoride, which is gaseous at comparatively low temperatures.
For reactors that do not use enriched uranium, the uranium oxide just has to be processed to uranium dioxide. However, for the enrichment facility, uranium dioxide then has to be further processed into uranium hexafluoride. The biggest risk in this particular phase of the nuclear fuel cycle is in the utilization of Hydrogen Fluoride.

Uranium hexafluoride once made is then pumped into huge metal cylinders, each with the ability to hold 14 tonnes. It is left for some time to solidify. These cylinders are then transported to enrichment facilities. The separation process splits the uranium hexafluoride gas into two streams: one of which is being continuously enriched to the required concentration (low-enriched uranium), and the other which is increasingly being exhausted of the Uranium-235 (tails).

The key enrichment process that is utilized in large scale production entails the use of centrifuges, composed of numerous fast-spinning tubes. The spinning action causes the two common uranium isotopes to separate based on their physical characteristics, particularly their one percent mass difference. The final phase of enrichment is known as laser enrichment - this results in enriched Uranium hexafluoride which is then converted back to enriched uranium oxide. At this stage the nuclear fuel material can be regarded as fungible, however nuclear fuel preparation entails a very particular outline (WNA, 2014). Enrichment Processes

Various enrichment methods have been demonstrated both historically and empirically; however, only two have been utilized on a large scale - the centrifugal process, and the diffusion process. Both of these processes entail the use of uranium hexafluoride as feed. The particles of U-235 and UF6 are both one percent less heavy than the rest of the molecules and it is this particular physical difference that forms the foundation of both enrichment processes. Enrichment of isotopes is a physical method (WNA, 2015).

The split streams of uranium hexafluoride produce low-enriched uranium and the "tails" (depleted uranium or DU). The former is used to produce nuclear fuel. The amount of DU is vital because it indicates the total work done to produce a specific amount of enriched uranium out of a given amount of uranium feedstock. Raw materials have different concentrations of Uranium-235 based on their location of origin. Unused mineral ores have about 0.7% concentration of uranium, while recycled uranium has about 1%; the depleted uranium has nearly 0.25% concentration. The size of an enrichment facility is determined with respect to its Separative Work Units (SWU). These are multi-part units that denote the energy produced, compared to the quantity of feedstock processed. Each SWU strictly measures in kilograms the amount of separation work done to enrich a particular quantity of uranium. The bigger unit-tonnes SWU-can also be utilized (World Nuclear Association, 2015).

Below are four of the main processes used in enrichment. They include: Diffusion, centrifuge, electromagnetic, and laser processes. Each of the processes has different features. The diffusion process is adaptable in response to fluctuations in demand and the cost of energy; however, it is highly energy intensive. The centrifuge process allows easy increase in capacity through modular expansion; it is however not highly adaptable. The laser process on the other hand has the ability to make the most use of depleted uranium by extracting the highest amount. It also has a capacity for modular expansion.

1. Centrifuge Process

This particular enrichment process was first used in the 1940s. It produces about 2 million SWU per year, making it economic and enabling the development of larger enrichment facilities. This process is highly energy efficient compared to the diffusion process; it requires only fifty to sixty kilowatt-hour per Separative Work Unit. Similar to the diffusion process, the centrifuge process utilizes Uranium Hexafluoride (UF6)…